1. Field of the Invention
The present invention generally relates to an image forming apparatus, an image processing method, and a computer-readable recording medium.
2. Description of the Related Art
Image forming apparatuses employing an electrophotographic method generally have a lookup table (LUT) for converting an image signal into a signal value in accordance with an engine characteristic, so as to obtain a suitable density gradation characteristic. Such an image forming apparatus is, for example, a color copier or a color printer using toner of a plurality of colors. In the case of a color copier, the LUT is provided for each of C, M, Y, and K colors. The LUT is optimized for each of C, M, Y, and K colors to allow a desired full color image to be output.
However, the characteristic of the electrophotographic method is likely to change in accordance with a surrounding environment or a status of use. Therefore, under fixed image formation conditions, it can be difficult to constantly output images of stabilized tone or hue using the electrophotographic method.
In order to obtain a suitable gradation characteristic, a method of forming a patch on a photosensitive drum, detecting a development density using the patch, and controlling image formation conditions (e.g., performing calibration) using the detection result is used. More specifically, the correction of a γ correction LUT and the change in charging condition or development condition of a photosensitive drum on which an electrostatic latent image is formed are performed.
However, in the above-described image forming apparatus in the related art, the patch formed on an image bearing member such as the photosensitive drum is provided in advance. In this case, the patch is formed for a stabilized toner color that typically does not require correction. Accordingly, it can take a long processing time to correct a γ correction LUT (e.g., to perform calibration).
Since calibration is performed for any type of input image using the same patch, it is not always possible to obtain an appropriate calibration result.
As described previously, if a patch for calibration is a fixed patch, it can be the case that calibration may not be performed for an important color in an input image. For example, if it is assumed that the input image includes a logo and only the color of the logo is to be stabilized at the time of image formation, then in this case, calibration may be performed using a patch having a color different from the color of the logo, and thus the color of the logo may not be accurately reproduced.